A review of thousands of FBI laboratory files has uncovered 27 death penalty cases in which experts may have exaggerated the reliability of hair analysis.

FBI lab reports dating back to at least the 1970s assert that hair analysis can’t be used to make a positive identification, but some FBI agents differed in their testimony, telling of near-certain matches, the Washington Post reports. The 27 death penalty cases are among 120 cases in which possible hair-analysis flaws have been identified.

The FBI and the Justice Department uncovered the cases in a review of more than 20,000 lab files that was undertaken in consultation with the Innocence Project and the National Association of Criminal Defense Lawyers, the story says. So far, about 15,000 files have been reviewed, turning up about 2,100 cases in which hair evidence was used and 120 convictions that could be problematic, including the 27 capital cases. The death-penalty cases will get the highest priority in further reviews; cases in which the defendant has already been executed will not be excluded.

The Justice Department will notify prosecutors, convicted defendants and their lawyers if a review panel finds FBI examiners made excessive claims. In such cases, the Justice Department will waive rules that restrict post-conviction appeals and will test DNA evidence upon the request of judges or prosecutors.

Those standards were hammered out in an agreement between the Justice Department, the FBI, the Innocence Project and the NACDL, according to the Post and a press release.